Redistricting in Maryland made Bartlett one of the nation's most vulnerable incumbents in the nation by adding a large swath of Democratic-leaning Montgomery County to his western Maryland district.

At age 86, Bartlett is the second-oldest member in the House of Representatives. He is one of just two Republicans among Maryland's eight House members. He was elected in 1992 after the longtime incumbent, conservative Democrat Bev Byron, was knocked off in a primary.

Delaney, a political newcomer, defeated state legislator Rob Garagiola in the Democratic primary to win this year's nomination.